1. Field of the Invention
The present invention relates to a fabrication method of LiCoO2 nano powder by a surface modification of a precursor.
2. Description of the Background Art
A secondary battery which is widely used uses LiCoO2 powder as the cathode materials. In fabricating the powder, a method of mixing lithium carbonate and cobalt trioxide and calcining the mixture at a high temperature is used. Such method is performed at higher than 800xc2x0 C. to obtain LiCoO2 of high temperature polymorph. In high temperature heating, growth of grain is occurred and in case of widely used powder, the size of the grain reaches 5xcx9c10 xcexcm. In addition, since the growth of the grain depends on contact state among grains, homogeneous grain size distribution of the grain which is finally obtained after calcining becomes very ununiform. Such characteristic is one of reasons that difference of powder characteristic for each batch for powder fabrication is caused.
In case the size of the grain is large, since removing/inserting rate of Li+ ion is relatively low in charging/discharging, it does not matter at a relatively low discharging rate, but capacity is faded at higher discharging rate. Also, there are many defections by broken bonds on the surface of the grain, and Li+ ions are trapped on the defective portion. Therefore, capacity fade is generated by charging/discharging.
In case the size and distribution of the grain are very uniform, there is an advantage that reproducibility in subsequent battery fabrication processes become excellent. Also, in case the size of the grain becomes smaller, the moving rate of the Li+ ion is relatively increased, and accordingly capacity fade according to high-speed discharging can be prevented, thus to enable manufacture of a high-output battery.
By the above reasons, there is an increasing demand for new LiCoO2 powder having a very small grain size and very uniform grain distribution.
Therefore, an object of the present invention is to provide LiCoO2 powder of a high temperature polymorph and a fabrication method thereof having a very small and uniform grain size.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a fabrication method of LiCoO2 nano powder, including the steps of preparing a Lixe2x80x94Co acetate precursor modifying a surface of the precursor by mixing the precursor with inert soluble salt obtaining LiCoO2 powder heating the surface-modified precursor, and removing inert soluble salt from the powder.
The inert soluble salt is selected among K2SO4, (NH4)2CO3, NaCl and KCl, and the amount of Li in the precursor is 100%xcx9c130%.
In the present invention, the LiCoO2 powder is obtained by cooling and drying by mixing initial materials, modifying the surface with an appropriate modifier, and heating the resultant material differently from the calcining method after simply mixing the conventional materials of the high temperature polymorph.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.